Topochemically controlled solid-state methyl rearrangement in thiocyanurates

2001 ◽  
Vol 57 (3) ◽  
pp. 428-434 ◽  
Author(s):  
Mark Greenberg ◽  
Vitaly Shteiman ◽  
Menahem Kaftory
Keyword(s):  
Solid State ◽  
Driving Force ◽  
Mirror Plane ◽  
Energy Calculation ◽  
Asymmetric Unit ◽  
Methyl Transfer ◽  
Plate Shape ◽  
Polymorphic Forms ◽  
Independent Molecules ◽  
The Difference

4,6-Dimethoxy-3-methyl-1,3,5-triazine-2(3H)-thione crystallizes in two polymorphic forms, needles and plates. In the needle-shaped crystals (9a) the molecules occupy the crystallographic mirror plane, thus the layers are stacked along the b axis. The molecules of the other polymorph [plate-shape crystals, (9b)] are packed in a herringbone packing mode. Upon heating, (9b) undergoes a phase transition to form (9a). At 378 K the needles undergo O → S topochemically controlled methyl transfer in the solid state to produce 1-methyl-4-methoxy-6-methylthio-1,3,5-triazine-2(1H)-one in 75% yield. The enthalpy of the rearrangement is estimated to be −39.1 kJ mol−1. 1-Methyl-6-methoxy-4-methylthio-1,3,5-triazine-2(1H)-thione crystallizes in space group P21 with two crystallographically independent molecules in the asymmetric unit. Compound (9b) undergoes O → S methyl transfer in the solid state at 373 K. The rearrangement is topochemically assisted and the product, 1-methyl-2,4-bismethylthio-1,3,5-triazine-6(1H)-one, is obtained in quantitative yield. The enthalpy of the rearrangement is estimated to be −58.8 kJ mol−1. The crystal structures of the compounds as well as their DSC thermographs are described and discussed. Energy calculation by ab initio methods shows that the driving force for the reactions is the difference between the molecular energies of the pre-rearranged compounds and their products, 54.2 and 59.3 kJ mol−1 in the two cases, respectively.

scholarly journals Structures of mono-unsaturated triacylglycerols. IV. The highest melting β′-2 polymorphs of trans-mono-unsaturated triacylglycerols and related saturated TAGs and their polymorphic stability

2008 ◽  
Vol 64 (2) ◽  
pp. 249-259 ◽  
Author(s):  
Jan B. van Mechelen ◽  
Rene Peschar ◽  
Henk Schenk
Keyword(s):  
Powder Diffraction Data ◽  
Asymmetric Unit ◽  
Double Chain ◽  
Molecular Conformations ◽  
X Ray ◽  
Acyl Chains ◽  
Independent Molecules ◽  
The Difference ◽  
Polymorphic Stability ◽  
Prime 2

The β_1^{\prime}-2 crystal structures of a series of mixed-chain saturated and trans-mono-unsaturated triacylglycerols containing palmitoyl, stearoyl and elaidoyl acyl chains have been solved from high-resolution powder diffraction data, from synchrotron as well as laboratory X-ray sources. The structures crystallized in the space group I2 with two independent molecules forming a dimer in the asymmetric unit, and packed in double-chain length layers. Unlike the corresponding β-2 structures the solved β_1^{\prime}-2 structures have different molecular conformations for the symmetric and the asymmetric mixed triacylglycerols, both with the sn-2 chain in a leg position of the chair-shaped conformation. A transformation to the β-2 structure with the sn-2 chain in the back position is complicated and unlikely to take place in the solid state. A novel β′-2 polymorph of PSS has been crystallized and its structure has been solved. The melting point (239 K) of this so-called β_0^{\prime}-2 polymorph is 2 K above that of the β_1^{\prime}-2 polymorph and almost equal to that of the β-2 polymorph of PSS. The difference in packing of the β_0^{\prime}-2 versus β_1^{\prime}-2 structure explains the slow β_1^{\prime}-2 to β_0^{\prime}-2 phase transition. The transition is strikingly similar to the β2-3 to β1-3 transition in cis-mono-unsaturated triacylglycerols.

9-(Methoxymethyl)anthracene

2007 ◽  
Vol 63 (11) ◽  
pp. o4442-o4442 ◽  
Author(s):  
Jie Liu ◽  
Guo-Hua Wei ◽  
Guang-Ju Ping ◽  
Jian-Fang Ma
Keyword(s):  
Hydrogen Bonds ◽  
Title Compound ◽  
Mirror Plane ◽  
Asymmetric Unit ◽  
One Dimensional ◽  
Compound C ◽  
Independent Molecules

The title compound, C16H14O, crystallizes with two independent molecules in the asymmetric unit, one of which lies on a crystallographic mirror plane. Intermolecular C—H...O hydrogen bonds link the molecules into infinite one-dimensional chains.

Cooperative Effects in Aminothiols: Acid-Base Equilibria and the Molecular Structure of 2-(N, N-Dimethylaminomethyl)thiophenol

2008 ◽  
Vol 63 (10) ◽  
pp. 1199-1203
Author(s):  
Holger Fleischer ◽  
Dieter Schollmeyer
Keyword(s):  
Molecular Structure ◽  
Aqueous Solution ◽  
Hydrogen Bond ◽  
Solid State ◽  
Ab Initio ◽  
Ab Initio Methods ◽  
Asymmetric Unit ◽  
Acid Base ◽  
Cooperative Effects ◽  
Independent Molecules

Abstract2-(N,N-Dimethylaminomethyl)thiophenol, (1, HL), is present as a non-zwitterionic aminothiol in the solid state, exhibiting an intramolecular S-H···N hydrogen bond. The S···N distances of the two independent molecules in the asymmetric unit are 2.929(10) and 3.050(10) Å. This structural feature is also present in an ab initio (MP2/6-31G*) optimized molecular structure. The investigation of the hydrogen bond by ab initio methods supports an n(N)-σ *(S-H) interaction as the reason for this bond type. On the basis of data from potentiometric acid-base titrations of a 0.01 M aqueous solution of [H2L]Cl with a 0.1 M aqueous solution of sodium hydroxide, values of 4.09±0.01 and 11.50±0.01 were obtained for pKa1 and pKa2 of [H2L]+. pKa1 is much smaller than pKa of thiophenol while pKa2 is bigger than pKa of benzyldimethylamine. The increased difference between pKa1 and pKa2 is attributed to the stabilization of HL by the intramolecular S-H···N hydrogen bond.

3-Oxoandrosta-4,6-dien-17β-yl 2-methyl-1H-imidazole-1-carboxylate and 3-oxo-5α-androst-17β-yl 2-methyl-1H-imidazole-1-carboxylate: C—H...π and π–π intermolecular interactions

2009 ◽  
Vol 65 (3) ◽  
pp. o88-o91
Author(s):  
Manuela Ramos Silva ◽  
Vânia M. Moreira ◽  
Cláudia Cardoso ◽  
Ana Matos Beja ◽  
Jorge A. R. Salvador
Keyword(s):  
Solid State ◽  
Ab Initio ◽  
Torsion Angle ◽  
Molecular Conformation ◽  
Asymmetric Unit ◽  
Compound I ◽  
The Mean ◽  
Independent Molecules ◽  
Compound Ii ◽  
Supramolecular Aggregation

The title compounds, C24H30N2O3, (I), and C24H34N2O3, (II), both contain an androstane backbone and a 2-methylimidazole-1-carboxylate moiety at the 17-position. Compound (I) contains two symmetry-independent molecules (denoted 1 and 2), while compound (II) contains just one molecule in the asymmetric unit. The C—C—O—C torsion angle that reflects the twisting of the 2-methylimidazole-1-carboxylate moiety from the mean steroid plane is 143.1 (2)° for molecule 1 of (I), 73.1 (3)° for molecule 2 of (I) and 86.63 (17)° for (II). The significance of this study lies in its observation of significant differences in both molecular conformation and supramolecular aggregation between the molecules of the title compounds. The solid-state conformations compared with those obtained theoretically fromab initiomethods for the isolated molecules show large differences, especially in the orientation of the methylimidazole substituent.

Polymorphic forms of lupane triterpenoid betulonic aldehyde (betulonal)

2014 ◽  
Vol 70 (9) ◽  
pp. 847-851
Author(s):  
Elwira Chrobak ◽  
Ewa Michalik ◽  
Joachim Kusz ◽  
Maria Nowak ◽  
Stanisław Boryczka
Keyword(s):  
Dimethyl Sulfoxide ◽  
Crystal Packing ◽  
Van Der Waals ◽  
Aldehyde Group ◽  
Geometric Parameters ◽  
Van Der Waals Interactions ◽  
Asymmetric Unit ◽  
Cyclopentane Ring ◽  
Polymorphic Forms ◽  
Independent Molecules

The lupane triterpenoid betulonic aldehyde [also known as betulonal; systematic name: lup-20(29)-en-28-al-3-one, C30H46O2] is a product of betulin oxidation. Crystals were obtained from hexane [form (I)] and dimethyl sulfoxide [form (II)] solutions. Forms (I) and (II) are both orthorhombic. The molecular geometric parameters in the two forms are similar, but the structures are different with respect to the crystal packing. Polymorph (I) contains two independent molecules in the asymmetric unit, while polymorph (II) contains only one molecule, which has a disordered aldehyde group [the disorder ratio is 0.769 (4):0.231 (4)]. In each molecule, the six-membered rings have chair conformations, whereas the cyclopentane ring in each molecule adopts an envelope conformation. All the rings in the lupane nucleus aretrans-fused. The extended structures of both polymorphs are stabilized by weak intermolecular C—H...O and van der Waals interactions. Weak intramolecular C—H...O interactions are also observed.

scholarly journals (Z)-5-(4-Bromophenyl)-3-{[(3,5-dichlorophenyl)amino]methylidene}furan-2(3H)-one

IUCrData ◽  
2020 ◽  
Vol 5 (7) ◽  
Author(s):  
Oksana A. Mayorova ◽  
Vyacheslav S. Grinev ◽  
Alevtina Yu. Yegorova
Keyword(s):  
Solid State ◽  
Title Compound ◽  
Crystal Packing ◽  
Large Cell ◽  
Monoclinic Space Group ◽  
Stacking Interactions ◽  
Asymmetric Unit ◽  
Compound C ◽  
Benzene Rings ◽  
Independent Molecules

The title compound, C17H10BrCl2NO2, crystallizes in the monoclinic space group C2/c with a large cell volume of 6207 (3) Å3. The asymmetric unit of the title compound investigated at 120 K contains two crystallographically independent molecules (Z′ = 2). Each molecule demonstrates slight non-planarity in the solid state and a Z-configuration for the exocyclic C=C bond. The crystal packing reveals the presence of π-π stacking interactions between the substituted benzene rings [centroid–centroid distances of 3.836 (5) Å, shift distances in the range 1.272–1.843 Å].

scholarly journals 3-Ethyl-1H-1,2,4-triazole-5(4H)-thione

2012 ◽  
Vol 68 (6) ◽  
pp. o1802-o1802 ◽  
Author(s):  
Bi Jing ◽  
Yuao-Chao Du ◽  
Ai-Xin Zhu
Keyword(s):  
Solid State ◽  
Hydrogen Bonds ◽  
Title Compound ◽  
Interplanar Distance ◽  
Mirror Plane ◽  
Stacking Interactions ◽  
Asymmetric Unit ◽  
Compound C ◽  
Π Stacking ◽  
Centroid Distance

The molecule of the title compound, C4H7N3S, exists as the thione tautomer in the solid state. The asymmetric unit consits of one molecule in which all atoms are located on a crystallographic mirror plane. In the crystal, adjacent molecules are linked by N—H...N and N—H...S hydrogen bonds into chains running along the a axis. π–π stacking interactions between the triazole rings [centroid–centroid distance = 3.740 (1) Å and interplanar distance = 3.376 Å] may further stabilize the structure.

Solid State and Solution Structures of an Adenine Analogue of the Antiviral Acyclonucleoside 9-(1,3-Dihydroxy-2-propoxymethyl)guanine

1990 ◽  
Vol 45 (7-8) ◽  
pp. 915-921 ◽  
Author(s):  
Joachim Granzin ◽  
Wolfram Saenger
Keyword(s):  
Solid State ◽  
Biological Activities ◽  
Monoclinic Space Group ◽  
Asymmetric Unit ◽  
Extended Form ◽  
Solution Structures ◽  
Cell Dimensions ◽  
Independent Molecules ◽  
Unit Cell Dimensions ◽  
C Nmr

Abstract The title compound. 9-(1,3-dihydroxy-2-propoxymethyl)adenine (DHP-Ade). an analogue of the antiviral acyclonucleoside 9-(1,3-dihydroxy-2-propoxymethyl)guanine (DHPG), crystallizes in the monoclinic space group P21. with unit cell dimensions of a = 10.848(4), b = 8.765(3), c = 11.432(4) Å. β = 102.14(3)° . with two independent molecules in the asymmetric unit. The crystal structure of DHP-Ade was determined and compared with that for DHPG. The solution conformations of both acyclonucleosides were also determined with the aid of 1H and ,13C NMR spectroscopy. In the solid state the acyclic chain may adopt a “folded” form, i.e. gauche about the C(1′)-O(1′) bond (as in DHP-Ade), or an “extended” form (as in DHPG), results which corre- spond to the rotations about this bond in solution. A general discussion is presented of the conformations of the acyclic chains of various acyclonucleosides, from the antiviral 9-(2-hydroxyethoxymethyl)guanine (Acyclovir, ACV) through to 2′,3′-seco-nucleosides, both in the solid state and in solution, and the relevance of these to biological activities.

Intramolecular and intermolecular geometry of thiophenes with oxygen-containing substituents

1999 ◽  
Vol 55 (6) ◽  
pp. 963-974 ◽  
Author(s):  
Alexander J. Blake ◽  
Bernard A. J. Clark ◽  
Hedi Gierens ◽  
Robert O. Gould ◽  
Gordon A. Hunter ◽  
...  
Keyword(s):  
Hydrogen Bonding ◽  
Solid State ◽  
Methoxy Group ◽  
Tautomeric Form ◽  
Nitrile Group ◽  
Two Dimensional ◽  
Asymmetric Unit ◽  
Liquid Samples ◽  
Independent Molecules

The intramolecular and intermolecular geometries of six thiophenes carrying oxygen-containing substituents have been determined. Crystals of 2-methoxythiophene and 3-methoxythiophene were grown in situ on a diffractometer from liquid samples. The 2-methoxy group introduces significant distortions to the thiophene nucleus and each molecule participates in four S...O contacts leading to an infinite bilayer. The extended structure of 3-methoxythiophene comprises zigzag chains of molecules linked by S...O contacts. Molecules of 2-acetyl-3-methoxythiophene are arranged in pairs about inversion centres, with ring centroids 3.835 Å apart. 5-Cyano-3-hydroxythiophene adopts the hydroxythiophene tautomeric form which allows conjugation between the S atom and the nitrile group: O—H...N hydrogen bonding leads to chains which are cross-linked by S...O contacts to give infinite two-dimensional layers. 5-(Methylthio)thiophen-3(2H)-one exists exclusively as the thiophen-3(2H)-one form in the solid state, allowing maximum conjugative interaction of both the ring heteroatom and the substituent with the carbonyl group: each molecule is linked to two of its neighbours through pairwise C—H...O interactions, forming ribbons. Spiro[cyclohexane-1,2′-2′,3′-dihydrothiophen]-3′-one crystallizes with four independent molecules in the asymmetric unit with only minor differences between these: the five- and six-membered rings in each molecule are approximately orthogonal and C—H...O hydrogen bonding generates chains. The last two structures differ from the others in that they lack a fully aromatic thiophene system.

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